Air quality within vehicles is an important, yet insufficiently addressed, issue. Passenger cars, public transportation vehicles, ships and commercial aircraft all have in common a confined space with high occupant density. Passengers consume oxygen and produce carbon dioxide (CO2) in significant amounts. Therefore CO2 levels tend to rise quickly, unless the air is replaced with relatively large amounts of clean, outside air, introduced into the vehicle.
Replacing the cabin air with outside air presents challenges of its own, both in terms of the cooling power required to condition the inflow of outside air as well as the quality of outside air surrounding the vehicle. The latter is especially true regarding high levels of fumes, smoke and dust that may be present in roadways and cities and including the exhaust emissions of other vehicles.
Most vehicles have systems designed to condition and circulate the air to provide a relatively comfortable environment for the passengers and, perhaps most importantly, the drivers or operating crew. These systems have provisions for replacing the air with outside air from outside the vehicle, while filtering and treating the outside air. However these are not always sufficient to provide good air quality, and face complex tradeoffs associated with the amount of outside air injected into the cabin. For example, most passenger cars allow air recirculation, so as to increase the efficiency of the air conditioner and avoid the introduction of outside fumes and dust.
Despite these provisions, air quality in vehicles can be quite poor. In particular, CO2 levels are found to be very high in passenger cars as well as in public transportation systems. For example, it was found that in a passenger car with four occupants and no outside air circulation, the CO2 concentration within cabin air of a closed cabin of the car, rises at a rate initially exceeding about 300 parts per million (ppm) per minute. After ten minutes of occupancy within the car, the CO2 concentration within cabin air was found to be higher than 2500 ppm. After thirty minutes of occupancy within the car, the CO2 concentration within the cabin air reached a concentration of about 4000 ppm, dangerously above the recommended CO2 concentration limit of 1000 ppm indoors.
The effects of elevated CO2 are only partly understood but it has been shown that even moderate elevation of CO2 has substantial impact on human cognitive functions, thus not only affecting the comfort and health of the passengers but also potentially diminishing the performance of the driver or operator and thereby creating a potential safety hazard.
The need for CO2 removal in passenger vehicles or public transportation has not been appreciated, let alone effectively addressed, and no practical solution has been proposed until now. This may be due to several reasons. Firstly, the impact of moderately-elevated CO2 on humans is not well understood, and its importance in a vehicle cabin even less so. Secondly, the problem only arises in a well-sealed vehicle with almost complete air recirculation, thus has been easy to overlook. And in addition, CO2 removal is a technically difficult challenge, much more so that simple air filtration, and practical solutions that can be cost effective in commercial vehicles has not been available until now.